docs: def write_bvec_file(bvecs, bvec_file):
      """
      Write an array of bvecs to a bvec file
  
      :param bvecs: array with the vectors
      :param bvec_file: filepath to write to
      """
      if bvec_file is None:
          return
      logger.info('Saving BVEC file: %s' % bvec_file)
      with open(bvec_file, 'w') as text_file:
          # Map a dicection to string join them using a space and write to the file
          text_file.write('%s\n' % ' '.join(map(str, bvecs[:, 0])))
          text_file.write('%s\n' % ' '.join(map(str, bvecs[:, 1])))
          text_file.write('%s\n' % ' '.join(map(str, bvecs[:, 2])))